v3.25.2
Investments - Ratings and Fair Value of Debt Securities (Details) - USD ($)
$ in Millions
Jun. 30, 2025
Dec. 31, 2024
Debt and Equity Securities, FV-NI [Line Items]    
Debt securities, available-for-sale $ 4,735.9 $ 5,131.0
Debt securities, trading 102.9 162.2
AAA    
Debt and Equity Securities, FV-NI [Line Items]    
Debt securities, available-for-sale 665.3 808.5
Debt securities, trading 29.0 74.0
AA    
Debt and Equity Securities, FV-NI [Line Items]    
Debt securities, available-for-sale 2,144.7 2,227.9
Debt securities, trading 32.2 54.0
A    
Debt and Equity Securities, FV-NI [Line Items]    
Debt securities, available-for-sale 1,032.5 1,375.0
Debt securities, trading 15.3 6.9
BBB    
Debt and Equity Securities, FV-NI [Line Items]    
Debt securities, available-for-sale 726.6 659.2
Debt securities, trading 24.0 24.2
Other    
Debt and Equity Securities, FV-NI [Line Items]    
Debt securities, available-for-sale 166.8 60.4
Debt securities, trading $ 2.4 $ 3.1